Glass manufacturing – Fiber making apparatus – Having coating or treating means
Reexamination Certificate
1999-06-17
2001-10-16
Vincent, Sean (Department: 1731)
Glass manufacturing
Fiber making apparatus
Having coating or treating means
C065S414000, C065S420000
Reexamination Certificate
active
06301936
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus for manufacturing a porous glass preform, and particularly to a structure of a reaction vessel of the apparatus in which glass particles are synthesized through a flame hydrolysis reaction.
2. Description of the Background
The porous glass preform is manufactured by depositing glass particles, as a core, and further, depositing glass particles thereon as a cladding. Typical methods for manufacturing the porous glass preform are an outside vapor deposition method (OVD) and a vapor-phase axial deposition method (VAD).
For example, the following is disclosed in Japanese Patent Laid-open Publication No. Hei. 5-330841:
A glass raw material made of oxygen, hydrogen, and silicon tetrachloride SiCl
4
) is fed to an oxyhydrogen burner. The oxyhydrogen burner produces an oxyhydrogen flame, and silicon tetrchloride (SiCl
4
) in a glass raw material is subjected to hydrolysis in the oxyhydrogen flame, so that glass particles containing silica (SiO
2
) as the main ingredient are produced. The glass particles are deposited, and finally become the porous glass preform.
Such manufacture of the porous glass preform is carried out in a reaction vessel. Japanese Patent Laid-open Publication No. Hei. 5-330841 also discloses this reaction vessel.
The reaction vessels are made of glass or metallic materials.
With the enlargement of the size of the preform in recent years, metallic materials (Fe—Ni, Ni—Cr or other Ni-based alloys, etc.) have come into conventional use. For example, Japanese Utility Model Laid-open Publication No. Hei. 3-74630 discloses a reaction vessel in which a wall is made of acid resistant metallic materials such as Ni or Ni-based alloy, and at least the inner surface thereof is coated with both heat and acid resistant paint.
The porous glass preform must be manufactured under a clean environment, so that impurities do not penetrate into the preform.
Further, the inside of the reaction vessel has a hydrochloric acid atmosphere. Therefore, the reaction vessel is required to have a degree of air tightness to prevent seepage of chlorine or any chlorine compound. In view of the above and also for the purpose of strength, an integral-type reaction vessel which is monolithically formed or which is constructed of several welded parts, has been used. As an optical fiber drawn from one porous glass preform is longer, production efficiency of optical fiber increases. Thus, the porous glass preform has become larger recently. Accordingly, the reaction vessel in which it is produced and contained has also enlarged. Further, during the manufacture of the porous glass preform, the temperature of an oxyhydrogen flame generated from an oxyhydrogen burner is in a range of 2,000 through 2,700° C., the temperature of deposited glass particles is in a range of 800 through 900° C., and the temperature of the reaction vessel wall is in a range of 300 through 400° C. With the enlargement of the reaction vessel the absolute amount of thermal expansion is increased, causing cracks or distortions in the reaction vessel.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an apparatus for manufacturing a porous glass preform for an optical fiber, which is not prone to be cracked or deformed by thermal expansion during the manufacture of a porous glass preform, especially the manufacture of a large porous glass preform.
A first embodiment of the invention is an apparatus with which a porous glass preform is manufactured by depositing the fine glass particles blown from a burner on a seed rod rotating around its axis and the reaction vessel of which is provided with means for relieving a stress caused to the reaction vessel due to its thermal expansion in the axial direction of the porous glass preform.
The apparatus according to the invention is characterized in that a reaction vessel to be used in the apparatus is provided with a means for relieving concentration of stress due to thermal expansion of the reaction vessel.
Thus, the occurrence of deformations or cracks of the reaction vessel can be restrained.
The second embodiment of the invention is an apparatus for manufacturing the porous glass preform which is characterized in that the said reaction vessel is set with the reaction vessel being held at portions other than the upper portion thereof in such a manner that the center axis of the porous glass preform is positioned in the vertical direction, and said reaction vessel is provided with fixing members around the periphery of the upper portion thereof for preventing its horizontal movement in a manner to allow it to expand and contract in the vertical direction.
Since the fixing members are disposed around the periphery of the reaction vessel, an escape margin of expansion toward the above is secured, the movement of a through hole in the horizontal direction can be prevented, the concentration of the stress can be relieved, and the occurrence of cracks can be restrained.
The third embodiment of the invention is an apparatus for manufacturing a porous glass preform which is characterized in that the said reaction vessel is arranged such that the center axis of the porous glass preform is positioned in the vertical direction, and the upper portion of the reaction vessel is divided into upper and lower parts having an insertion structure which allows the reaction vessel to expand and contract in the vertical direction.
Since the reaction vessel is divided into the upper and lower parts at the upper portion of the reaction vessel, and the insertion structure is adopted as described above, an escape margin of expansion toward the above can be secured, the movement of a through hole in the lateral direction can be prevented, the stress can be relieved, and the occurrence of cracks can be restrained.
The fourth embodiment of the invention is an apparatus for manufacturing the porous glass preform according to the third embodiment, which is characterized in that the insertion structure portion of the divided parts is provided with a means for allowing a purge gas to flow.
With this invention, in the case where the reaction vessel is divided into the upper and lower parts, the entrance of air containing dust through the divided parts can be prevented.
The fifth embodiment of the invention is an apparatus for manufacturing a porous glass preform which is characterized in that the said reaction vessel is set such that the center axis of the porous glass preform is positioned in the vertical direction, and is held with the fixing members for allowing said reaction vessel to expand and contract in a vertical direction, and for restraining the reaction vessel from moving in a horizontal direction.
Since the fixing portions of the reaction vessel are fixed in a state where the reaction vessel can expand and contract in the vertical direction, the escape margin of expansion toward the above can be secured, the movement of a through hole in a lateral direction can be prevented, concentration of stress can be relieved, and the occurrence of cracks can be restrained.
The sixth embodiment of the invention is an apparatus for manufacturing a porous glass preform which is characterized in that said reaction vessel is set such that the center axis of the porous glass fiber is positioned in a horizontal direction and the reaction vessel is held with a plurality of fixing members allowing its expansion and contraction to the axial direction of the center axis of the porous glass fiber and preventing its horizontal movement.
Since the reaction vessel is fixed in the state where the vessel can expand and contract in a longitudinal direction as described above, the escape margin of expansion in a longitudinal direction can be secured, a movement of a through hole toward the side of the vessel is prevented, stress can be relieved and the occurrence of cracks can be restrained.
A seventh embodiment of the invention is an apparatus for manufacturing a porous glass preform which is characterized in that th
Kogo Takashi
Ohga Yuichi
McDermott & Will & Emery
Sumitomo Electric Industries Ltd.
Vincent Sean
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